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The Cosmic Origins Spectrograph (COS, pictured) will probe the "cosmic web", described by NASA as "the large-scale structure of the universe whose form is determined by the gravity of dark matter and is traced by galaxies and intergalactic gas".

COS will examine how this web "evolved from ancient times", as well as sampling "the chemical content and physical state of gas in distant galaxy halos" to provide an "important insight into the building process of early galaxies and the production of elements heavier than hydrogen and helium over cosmic time".

To accomplish its goals, COS boasts "extraordinary sensitivity" in its far-ultraviolet channel, quantified as "a factor more than 30 times greater than that of previous spectroscopic instruments for the detection of extremely low light levels".

NASA amplifies: "COS has two channels, the Far Ultraviolet (FUV) channel covering wavelengths from 115 to 177 nm, and the Near Ultraviolet (NUV) channel, covering 175-300 nm. Ultraviolet light, the type of radiation that causes sunburn, is more energetic than visible, optical light. 'Near' UV refers to the part of the UV spectrum closer to the visible, just beyond the colour violet.

"The light-sensing detectors of both channels are designed around thin micro-channel plates comprising thousands of tiny curved glass tubes, all aligned in the same direction. Simply described, incoming photons of light ultimately induce showers of electrons to be emitted from the walls of these tubes. The electron showers are accelerated, captured, and counted in electronic circuitry immediately behind the micro-channel plates."